1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
In conventional wireless communications, one or more mobile units (or access terminals) may establish a wireless link to a Radio Access Network (RAN). The RAN architecture is typically hierarchical and call state information associated with each mobile unit's session is stored in a central repository, such as a Radio Network Controller (RNC), a Packet Data Serving Node (PDSN), and the like. One alternative to the conventional hierarchical network architecture is a distributed architecture including a network of base station routers. For example, each base station router may combine RNC and/or PDSN functions in a single entity that manages radio links between one or more mobile units and an outside network, such as the Internet. Compared to hierarchical networks, distributed architectures have the potential to reduce the cost and/or complexity of deploying the network, as well as the cost and/or complexity of adding additional wireless access points, e.g. base station routers, to expand the coverage of an existing network. Distributed networks may also reduce (relative to hierarchical networks) the delays experienced by users because packet queuing delays at the RNC and PDSN of hierarchical networks may be reduced or removed.
Distributed architectures allow one or more mobile units to establish a session with any one of the plurality of base station routers. To establish a session, the base station router negotiates session parameters with the mobile unit and assigns an identifier, such as a Unicast Access Terminal Identifier (UATI), to the mobile unit. For example, a proposed Code Division Multiple Access (CDMA) protocol standard for packet data transmission, sometimes referred to as the EVolution-Data Only (EVDO) standard, specifies a unique 128-bit UATI that is assigned to a mobile unit when a session is initiated by the mobile unit. The mobile unit maintains the UATI for the duration of the session. In the current implementation, the EVDO session UATI is divided into two parts: a 104-bit UATI104 and a 24-bit UATI024. The UATI024 portion is unique to the mobile unit for the duration of the session and the UATI104 is common to all mobile units within a predetermined subnet of base station routers in the distributed network. During negotiation and granting of the session, the base station router allocates resources, such as system memory, to the mobile unit. Negotiation of the session parameters and allocation of the resources to the session consume processor bandwidth in the base station router and other entities in a wireless communication system.
In operation, base station routers in a conventional distributed network may broadcast, or advertise, their subnet address, e.g. the address indicated by the UATI104 portion of the UATI. However, the address is generally too long for mobile units to insert in the user identification portion of each message sent to the base station routers, so the base station routers also typically advertise a color code for use by the mobile station, which is typically an 8-bit representation of (or alias to) the 104-bit UATI104 subnet address. The base station router providing service to the mobile unit may change, e.g., due to fluctuating channel conditions and/or when the mobile unit roams between different subnets in the distributed network. Accordingly, mobile units may determine whether or not the subnet including the base station router providing service to the mobile unit has changed by monitoring the advertised subnet address on the control channel. Mobile units may request a session transfer between subnets based on the detected changes in the color codes.
Additional system resources may be consumed when a mobile unit and the associated session are transferred between subnets. For example, mobile units typically request a session transfer from the old subnet to the new subnet when the mobile unit detects a change in the subnet address broadcast by nearby base station routers. For example, a mobile unit may initiate a session with a first base station router belonging to a first subnet having a first subnet address. The first base station router assigns a UATI to the mobile unit. When the mobile unit becomes associated with a second base station router belonging to a second subnet having a second subnet address, the mobile unit may request, using the associated color code, that its previous session information be transferred from the first base station router to the second base station router. The memory allocated to the mobile unit may also be transferred to the second base station router. All of these processes consume processor bandwidth at both the source and target locations.
In order to utilize services provided by a wireless communication system, the mobile unit associated with a session must request and establish a connection. For example, a mobile with an existing session may transmit a request for service to the wireless communication system and the system may establish a connection in response to the request. Establishing the connection typically includes negotiating various parameters according to one or more protocols, such as the Point-to-Point Protocol (PPP), between the mobile unit and a wireless communication system. Once the session and the connection have been established, the mobile unit can exchange packets with the wireless communication system. For example, a mobile unit and the system may exchange Internet Protocol (IP) datagrams with hosts in the Internet when both a session and a connection have been established.
Mobile units that have established sessions with the wireless communication system do not necessarily utilize the available services and therefore do not necessarily establish connections associated with these sessions. To the contrary, the vast majority of mobile units that establish a session with the current 1×EVDO system rarely or never establish a connection to the system. For example, only 3% to 10% of the mobile units having sessions with currently deployed EVDO systems are believed to ever establish a connection to access the services provided by the systems. An even smaller percentage of the mobile units are believed to be frequent users that maintain a connection for a large percentage of the lifetime of the associated session. Consequently, a significant quantity of system resources may be allocated to sessions that rarely or never have any need of these resources, which may deprive other users of system resources, particularly when the system is heavily loaded.
Previous proposals to reduce processing and memory usage/paging have taken the form of software optimization techniques, such as time-consuming “memory mining” activities that may become more efficient with memory use. Additional functionality may also be added to reduce the number of idle transfers, features such as RNC Grouping, or increasing the size of subnet areas. This latter feature reduces the number of idle transfers at a cost of increasing the paging load, which requires another feature to reduce the paging area. This feature, however, has an additional side effect that mobile units may send route update messages more often, and the information from the route update message will have to be stored with the session information, using memory and processing. None of these techniques directly address the problem of users that rarely use the system.